The World Wide Web (WWW) contains web pages that use both Hyper-Text Markup Language (HTML) and Cascading Style Sheets (CSS). Over the past several years, HTML has become the predominant markup language for the creation of web pages. It describes the structure and style of text-based information in a document and supplements that text with forms, embedded images, and other objects. Meanwhile, CSS is a popular style sheet language used to describe the presentation (e.g., colors, fonts, layout, etc.) of documents written in markup language. By using HTML and CSS together, web designers are able to advantageously separate a document's structure and content (written in markup language) from its presentation formatting (written in style sheet language).
Generally speaking, web pages are viewed using web browsers. Web browsers interpret HTML and CSS elements of a web page, and render the web page to a user. There are many web browsers available today, including, for example, Microsoft Corp.'s INTERNET EXPLORER®, Mozilla Corp.'s FIREFOX®, Opera Software ASA's OPERA®, Netscape Communications Corp.'s NETSCAPE®, and Apple Computer Corp.'s SAFARI®, among others. When creating web pages, designers frequently use validation tools that automatically check HTML and CSS code for invalid tags, attributes, or values. Such validation tools are sometimes included in application development environments such as, for example, Adobe Systems Inc.'s DREAMWEAVER® and GOLIVE®.
Unfortunately, the lack of coding errors does not guarantee pixel-perfect rendering across all browsers. In fact, certain rendering problems involve complex relationships between HTML elements and CSS properties. As a result, even after HTML and CSS code is otherwise validated, different web browsers may still render or display the same web page differently.